Plicopurpura pansa is a cultural resource with economic importance since ink can be extracted from it to dye clothes. This snail inhabits the rocky intertidal zone of Mexican Pacific, is found attached to rocks in crevices and holes. The objective was to analyze the P. pansa population structure in Costa Chica of the State of Guerrero based in density, sex ratio, size and weight, besides to realize observations on mating and recruitment, for which quarterly sampling was made during an annual cycle in three beaches. The density was 4.83 snails/m2. Sex ratio ranged from 0.76:1.00 to 1.00: 0.96 (F:M). Average size was 20.91 mm. The best represented sizes in females were from 10.5 to 28.5 mm and in males 13.5 to 28.5 mm. Averaged weight was 1.99 g, females showed a coefficient of variation in weight of 96.53%. Recruitment occurred for the entire year. In December 2006 and September 2007 a larger frequency of recruits was shown. Sex ratio showed a 1:1 tendency. Snail population was characterized by being small sized and in high densities. Weight variations in females were found related to their reproductive cycle.